When I try to move a file on my desktop to a folder (opened using Files), the file will not go into it. If I move it to a folder using the mouse pointer, it moves back to the desktop when I release the mouse button. If I right-click on the file, there is no "Move to" option on the menu. This also applies to external drives (e.g. expansion drive, flash drive stick). I have had this problem for a number of months now.